Students from the alternative school helped remove internal supports after the shotcrete work.
I squared and leveled the PVC forms for the four posts that make up the inner "circle."
There are four pads at the center, twelve around the perimeter, plus two more for the doorway.
We peeled the support logs and cross beams with a Log Wizard.
Support posts in place.
The main framework for the earthlodge complete with support logs and cross beams secured in place.
Adding a perimeter foundation around the earthlodge.
I closed in the doorway with slabwood boards of many different sizes.
Additional beams were needed at the four "corners" of the cirlce.
Filling in the roof with slabwood.
View from inside the earthlodge.
Forklift loading a slabwood bundle in the truck.
Trimming slabwood to fit the angles.
Closing in the walls.
Almost done with the first layer, we added smaller pieces to fill the gaps.
Covered with carpet and tarps for the winter.
Inside the earthlodge.
In some places the bottom of tthe carpet is visible in the ceiling.
Skylight window frame.
We dug a trench for a footing and added reinforcing bar and welded wire mesh over the dome.
Formwork for the footing.
Freshly poured concrete.
View of the earthlodge across the reflecting pond.
Wire-tying the rebar to the earthlodge.
Temporary supports to hold up the roof for shotcrete work.
Temporary wall supports.
The shotcrete hose was too much for one person to handle alone.
A three-person crew is ideal to hold the shotcrete hose.
Covering the earthlodge with shotcrete.
Spraying shotcrete from the top of the cement truck.
Completed shotcrete work.
Building a Modernized Earthlodge
Exploring Low-Cost Dome Construction Methods
by Thomas J. Elpel, Author of
Living Homes and
Participating in Nature
I burned my old earthlodge to the ground. It was a 23-foot diameter igloo-like structure built with poles and covered with straw and earth, as shown in my book Participating in Nature. It was a great shelter. I could take the kids camping in the middle of winter, and it was t-shirt warm, with room to work on projects or just hang out someplace other than the house. But it had its problem's too. The roof pitch wasn't as steep as it should be, so smoke hit the ceiling and stacked downward until we were laying on the ground gasping for air. And water worked through the earthen cover and rotted the poles until it wasn't safe to use after five years.
Removing the earthlodge presented a unique challenge. Fortunately, my brother was reroofing a church in town and needed to dispose of the old cedar shingles. We loaded the shingles into the earthlodge then waited for a snowy day to light the match. The flames shot out the smoke hole twenty feet into the air, and the ground smoldered and smoked for a month afterwards, but it successfully burned virtually all wood in the shelter. Final cleanup required little more than raking the site flat and broadcasting some seed to reclaim the bare ground.
I missed the earthlodge, and fifteen years went by without one. We eventually bought a 21-acre river property for our wilderness survival programs, and I decided to build a new, bigger earthlodge on site to use as an all-weather classroom facility. This time, however, I wanted to build a permanent earthlodge with a cemented dome, which should hopefully last a century or more. The goal was to make something that looks primitive inside and out, but is actually a modern structure with the wooden members fully separated from the soil to prevent rot. In addition to making a cool classroom, the project was an excuse to experiment with low-cost dome housing alternatives as proposed in my book Living Homes: Stone Masonry, Log, and Strawbale Construction.
Earthlodge architecture comes from the northern Great Plains where Mandan Indians built massive structures for communal housing and shelter from bitterly cold subzero winters and the relentless wind of the Plains. The initial framework for an earthlodge looks something like Stonehenge, or rather "Woodhenge," with an inner and outer circle of support poles topped by cross beams connecting everything together. The bottoms of the support poles were buried in the earth to secure them vertically. Lacking nails, spikes, or screws, they selected forked poles to lock everything together without hardware. This wooden skeleton was covered with a solid layer of small diameter poles to close it in. A layer of brush and straw on top of the earthlodge helped spread the weight of the eventual earth load. The brush also probably facilitated air circulation around the wood in the roof to prevent rot. Living in the shelter full time and using a daily fire also probably helped dry and smoke the wooden ceiling to prevent rot.
There is deep wisdom in earthlodge architecture. Dome-shaped structures are inherently strong, great for supporting an earthload, and also durable against tornados, earthquakes, and just about anything else Mother Nature can throw at them. In addition, burrowing into the earth, or building up and covering a structure with earth, is one of the most effective ways to protect a dwelling from extreme heat, cold, or wind. Besides my interest in earthlodges, I've also been interested in monolithic dome homes and other dome-construction methods, so it seemed logical to marry the two interests to make an earthlodge with a cemented dome.
As a potential home, this modernized earthlodge seemed like a good way to erect a spacious, weatherproof abode in a season on a limited budget. That could be especially helpful for any young couple that saves enough money to buy land, but doesn't yet have the time, money, or skill to build a regular house. They could potentially erect an earthlodge-like structure with a cement dome and create a functional, hopefully low-cost home to live rent-free and mortgage-free. They could always add additional dome rooms later or build a more conventional home if so desired.
Inspired by Hobbiton in New Zealand, I thought it would be cool to axe the igloo-like tunnel and chop off one side of the earthldoge to make a flat wall with a round door and windows like a Hobbit home. Unfortunately, that would not be consistent with the primitive decorum I wanted for our wilderness survival field camps, so I chose to stick with traditional earthlodge architecture, at least in shape.
Another design factor was material availability. The original earthlodge built at my home required numerous trips into the mountains to cut all the poles for the skeleton and covering. The new site was twenty-five miles farther from the mountains, and the new earthlodge would be larger, 34-feet in diameter instead of twenty-three. That would require many, many trips back and forth to the mountains to gather materials, as well as a lot of labor, more than I was willing to ask of the interns in our Green University® LLC program. Instead, we cut and hauled only enough logs for the main structural components, which we accomplished in two big pickup loads.
For the roof poles, I chose to substitute slabwood purchased from a sawmill four miles from the construction site. The flat slabs are not as strong as round poles for supporting an earthload, but they didn't need to be for this modified earthlodge. The wooden structure only needed to be strong enough to support the fresh cement work. The goal was to make a cement dome that is structural in itself, and the dome would support the earthload. The interior woodwork serves structurally only as formwork for the cement, but would be left in place for cosmetic reasons, to have a beautiful, neoprimitive wood interior inside the cement dome.
The final dimensions of the earthlodge were dictated by the length of the slabwood, which was mostly pre-cut to approximately 8 to 10 feet long. The distance between the inner and outer support rings had to be no more than eight feet to bridge across them with slabwood. Additional space is created outside the skeleton, where the slabwood slopes down to the ground to form the walls. Add in several feet for the inner ring where the smokehole is, and we ended up with a total diameter of 34 feet.
Our property is along the Jefferson River in southwest Montana, and the whole of it is in the floodplain, but protected by an earthen levee. We were fortunate to tour the property during the floods of 2011 to see the property during an extreme high water year. The levee holds the river back, but the ground is all sand and gravel, so water equalizes on both sides of the levee. A pond in front of the future earthlodge filled to the brim and flooded part of the field. There were shallow puddles in the road. Overall, not too bad considering how high the river was. We placed the earthlodge on the highest, driest part of the property, on equal elevation with an old railroad bed that used to cross through the place. The earthlodge is near the entrance gate and parking lot, serving as a transitional space between the modern world behind it and the primitive camp in front of it. The structure faces the east towards the morning sun, as is traditional among many native dwellings. And the reflecting pond out front aligns well with Feng Shui design principles.
Earthlodge construction could have easily been completed in a single season, so that the builder could move into it and use it right away. However, I have many competing projects and was in no particular hurry on this one, so we stretched construction out over several years (still ongoing) as time, labor, materials, and money allowed.
The project began in the fall of 2014. Rather than burying support poles in the earth where they would rot off, I decided to use concrete pads to separate the poles from the dirt. We were planning to pour a concrete floor inside an existing shed on the property, so I combined the two projects in one pour. I cut oversize scrap PVC pipe into 8-inch lengths to use as forms for the concrete pads for the earthlodge. I laid these forms out on the ground where the support poles would go, measuring, squaring, and rechecking everything multiple times. I used a four-foot level strapped to a board to compare one PVC form to another, digging down as necessary to level all the pads to each other. By itself, the volume of concrete needed wasn't enough to justify calling in a concrete truck, but it was easy to add a little bit to the load needed for pouring the shed floor. We did that project first then used the remaining concrete to fill the PVC forms. I troweled each pad smooth, then inserted a foot-long length of ?-inch rebar into each pad to anchor the eventual support logs in place.
Up in the mountains, we cut two big truckloads of lodgepole pine and Douglas fir for the support logs and cross beams. Back at camp, we used a Log Wizard to peel the logs. It is essentially a planar blade that attaches to a chain saw. Walk backward dragging the Log Wizard down the log, and it shaves off a strip of bark. It doesn't take long to peel an entire pole this way, and only a few hours work for one person to peel all the poles.
Green University interns assisted with cutting, hauling, and peeling the logs. They moved onto other projects while I did most of the structural framework. I drilled a hole in the bottom of each support pole then set them down on the rebar pins embedded in the concrete pads. I started with the inner "circle," actually a square of four tall posts capped with connecting logs. The support poles were leveled and secured with scraps of slabwood nailed or screwed to the wood and braced against each other and the ground.
The outer circle required angle cuts for the cross beams on top of each post. It seemed easiest to secure the logs in place then cut the excess off from a ladder with the chainsaw. Everything is pinned together with very large nails or spikes.
My mobility was limited by a torn ACL in my left knee from a year before, but I was able to carefully and slowly work on the earthlodge framework until I went in for reconstructive surgery in early October. Knee surgery ended work on the earthlodge for the year.
By January of 2015 I had some mobility, and we were blessed with unusually dry, warmish weather, so my friend Jeff and I started work on the perimeter "foundation" to separate the slabwood walls from the dirt. I had a big pile of solid triangular concrete blocks from the scrap pile at the local cement block factory, so we dug and leveled a trench around the earthlodge and laid the blocks in around the perimeter. Winter, travel, and other distractions took me away from the project until May, when I finished the perimeter foundation. The circular dome is designed from a square center, and additional supports were needed to fill in the triangles in the roof, so I added support beams at each corner.
In October 2015 we finally returned to the earthlodge to close it in with slabwood. Slabwood is the leftover scrapwood after a sawmill cuts square boards out of round logs, and they sell it primarily as firewood. A bundle costs $65 at the local sawmill, and they load it in the truck with a forklift. Each bundle includes a mix of short and long slabwood, plus various scrap boards that were cut flat on two, three, or four sides. About two-thirds of the slabwood in each bundle was useful for our project; the rest we set aside for firewood. I ordered six bundles in the course of the project.
Bartle and Janeth working on the walls.
After the slabwood, we covered the earthlodge with relatively clean carpet scavenged from a nearby dumpster. I chose carpet as a no-cost way to cover the structure and bridge over any gaps between the slabwood. The bottom side of the carpet has a texture and color similar to a burlap sack, so it looks natural enough if seen between the cracks from inside the structure. It also provides a small amount of insulation, and it would eventually separate the cement dome from the woodwork to reduce condensation concerns that might rot the wood. Next, we covered the earthlodge with plastic and tarps so that students could move into the structure and use it for living quarters for winter classes. So far so good; we had a functional structure, and the total cost for concrete, hardware, and slabwood was about $500!
We returned to the project in the spring of 2016 and started preparing for the biggest step of the building process--applying wire reinforcing and cementing the dome. First we removed the tarps and plastic, leaving the carpet in place, and I built a window frame from scrap lumber for the apex of the structure. In the short term, it serves as an oversized smoke hole, but the ultimate plan is to have a funnel-like hood over the fire with a chimney pipe out the top, plus a Plexiglass skylight to trap heat inside during winter and mosquitos out in summer.
I hoped to wrap the earthlodge with recycled wire mesh and spray a thin coat of sand and cement mortar over it to form a strong dome. Ideally, the cement dome would have connected to the cement block perimeter foundation, except that the slabwood covered the foundation entirely. This plan was not well-researched in advance of the project.
I assumed that someone local could come spray a couple inches of mortar over the dome, but the only "local" applicators lived several hours away. I started working with a shotcrete company out of Red Lodge, Montana and necessarily followed their advice to prepare the project. I didn't mind taking their advice. They are the experts, and if I hoped to hire them, I needed to make sure the project conformed to their specifications.
Issue number one, the cement dome needed a footing for support, and since the slabwood covered the concrete blocks, we had to dig a trench around the earthlodge, lay in reinforcing bar, and pour a concrete footing. Also, they said I needed to cover the structure with heavy duty welded wire mesh, normally used in flat concrete slabs, plus 3/8-inch rebar vertically every foot around the structure. Fine. That added some cost and labor, but no worries there. I did not have a source for the recycled wire fencing I had hoped to use anyway. Working with Green University instructors, interns, and my girlfriend Janeth, we quickly dug the footing, installed a cage of metal all over the earthlodge and called a concrete truck to pour the footing, adding $480 to the project cost.
Sending photos to the company, they advised that we also needed 3/8-inch rebar spaced horizontally every foot up the structure. Perhaps I missed that in an earlier conversation. No worries, we added more rebar. Any rebar that stuck up too high we secured to the earthlodge with wires and screws stuck through the carpet into the slabwood. Rebar or welded wire mesh that laid flat on the carpet was initially propped up with stones to allow the mortar to flow around and encase the reinforcing mesh. Later I rediscovered a bucket of plastic rebar supports which I long ago salvaged from a dumpster. Those were much easier to work with than rocks to raise the rebar off the carpet. Inside the earthlodge, we installed dozens of temporary supports to reinforce the roof and walls for the shotcrete work. All the steel, wire ties, tools, and hardware added $830 to the project cost, for a running total of about $1,810. I knew the shotcrete would add considerably more, but one way or another, the project would move forward.
I had imagined applying mortar a couple inches deep, but the professionals recommended six- to eight-inches thick at the base tapering to three- or four-inches at the top. Nor had I really grasped the scale of the project. A thirty-four-foot dome (more like thirty-six-feet on the outside), is a very large structure, and the math added up to more than twenty, potentially up to thirty yards of shotcrete to cover the entire earthlodge depending on thickness. I have built a couple of sizeable houses, yet this neoprimitive project would consume more energy-intensive, expensive mortar than any single previous concrete pour I have done.
A representative for the shotcrete company stopped by one day to see the project. He confirmed that it looked good inside and out, and they could fit the project in their upcoming schedule. Great! I was looking forward to hiring someone to do a job for once, rather than doing everything ourselves. He measured the structure then went home and ran the numbers. The official bid for bringing a crew out to spray shotcrete on the earthlodge: $28,000!
I've done this before. I frequently get the idea to hire out a project or to purchase something prefabbed, but sticker shock sweeps me back to do-it-yourself reality. There is a reason why I built, wired, plumbed, and finished my own home, and a couple others. Necessity is not only the mother of innovation, but also the mother of do-it-yourself inspiration. I knew we could rent a shotcrete machine and do the job for a fraction of the company bid. But we had to set the project aside for the summer and come back to it when we had more free time in the fall.
Fortunately, my sister's friend Larry owns a shotcrete machine, which he uses for mining work in nearby Butte, Montana. The shotcrete machine includes a hopper to pour the mortar into, and a pump to push it out a hose. The machine is built onto a trailer, so we hitched up and towed it back to River Camp with my truck. Shotcrete also requires an oversized air compressor, which connects to the end of the hose to spray the mortar. The diesel-powered air compressor is also a trailer, requiring a second trip to the mining city. We were fortunate in that there wasn't a time crunch to set up the equipment and apply the shotcrete. We paid $500 to rent all the equipment, which I think was a good deal. We did the setup work one week, then called the local cement plant to deliver mortar for shotcrete the following week.
After studying shotcrete formulas online, we chose to go with 4 parts sand to 1 part pea gravel, with 8 sacks of cement per cubic yard. I ordered some Kel-Crete admixture in advance, which facilitates flow through the hoses in extremely small amounts. I had some concrete dye previously salvaged from a dumpster, which I dropped off at the cement plant. A two-gallon bucket of earth-toned dye for each five-yard batch of shotcrete wouldn't add much color, but I hoped for something better than cement grey. The cement plant had plastic fibers on hand, which we added to the mix for additional strength. For simplicity, I ordered five loads of five yards each, to be delivered over four days so we could layer the structure up a little at a time and not collapse it from too much weight. The cost? $140/yard or $3,500 for the whole project, assuming everything went as planned.
We scheduled the project for early October when there would be plenty of friends, instructors, and interns around to help out with the project. We were told that it takes several people just to drag around the heavy hoses full of concrete. My sister Jeanne came along too, and she has a mechanical aptitude that I sorely lack. She ran the shotcrete machine and the air compressor, and she communicated directly with the delivery driver about when to start or stop adding mortar to the hopper. In other words, she pretty much ran the show, for which I was immensely grateful. Larry helped out the first day to get us started with the equipment, which was also immensely helpful, since the rest of us had zero experience.
Unfortunately, the opening scenes were disastrous. I took the first crack at running the shotcrete hose to spray mortar on the earthlodge. I held the hose, and they turned on the pump and air, and out came the shotcrete. I couldn't hold or aim the hose by myself, and before we could figure out what was going on, a surge jolted me sideways and sprained a tendon on the back of my knee, my good knee. I landed on the ground in pain, not knowing how bad I was injured. Jerry got control of the hose, and as we quickly learned, we had to have two more people standing right behind him to help hold the hose. Five minutes into the project, and I was already out for the count, useless aside from relaying signals and taking pictures. I am immensely grateful for having such awesome help that everyone was able to pick up and carry the project through to completion!
A five-yard load shoots out amazingly quickly, and in forty-five minutes we were done and beginning cleanup work, which takes just as long. It would have been nice to apply batch after batch without cleaning in between, but we couldn't risk adding too much weight to the earthlodge at any one time, at least not until the base layers began to harden and solidify the structure.
In the initial mayhem, we were spraying shotcrete over the earthlodge towards the cement truck, shotcrete machine, air compressor, and operators. Behind all of them, a small piece of gravel shattered the side window on my car. Add that to the project cost! I moved my car farther away, and we used a sheet of plywood and tarps to better protect Todd, the cement truck driver. Most of all, the crew tried to be more conscientious about where the hose was pointing and what was beyond the target area.
Spraying the walls was relatively easy. Spraying the top of the dome was more challenging, and we hemmed and hawed and debated the best way to do that. Our initial idea was to build a platform on the back of my truck to get the hose operator five feet off the ground. They could stand on the platform and we would drive forward a little at a time around the structure. But after seeing the pressure involved, we knew it wouldn't be safe for anyone to stand on a platform like that. We considered bringing in a lift or bucket system to safely get the elevation needed to spray the dome, but nothing came together. Fortunately, we were able to spray much of the dome from the ground by merely pointing the hose upward, being mindful of what lay beyond the target. We sprayed quite a bit of shotcrete into the willows trying to hit the chimney.
At Todd's suggestion, we strapped the hose to the upper deck of the cement truck, securing it so that one person could control it. That worked well on one side of the earthlodge, but Todd had to stay close enough to the shotcrete machine to pour mortar into the hopper, so we couldn't move far from that one position. Therefore, we did most of the dome from the ground. It was difficult to obtain an even application from ground level, but Jerry did a masterful job under the circumstances. He ran point for four of the five batches before he had to return to work. Neal took over for the final batch and applied the finishing touches. Arguably, the job could have used another five-yard batch to thicken it up and even out some places, but we did what we could with what we had. We used up all the Kel-Krete, most of the dye, our workweek, and all of our help. It was definitely time to quit!
We cleaned up and hauled the equipment back to Butte the same day. The following week we removed the temporary supports from inside, making the earthlodge ready to use for the winter. The running total so far (excluding gas and the broken car window) adds up to $5,810. That is more expensive than I hoped for, but still not outrageous for 900 square feet of enclosed space.
Is the earthlodge complete? Nope. Absolutely not. A few days after the shotcrete, we stopped by and Janeth watered the entire structure with a hose, twice. Cement needs water for the chemical reaction that turns mortar into stone, and the fresh cement was hyper thirsty for water after a couple of unusually warm October days. A five-gallon bucket of water sloshed onto the shelter would be completelu absorbed by the cement before it reached the ground. Cement also remains highly porous, so it will be necessary to waterproof the structure to avoid saturating the cement and rotting the carpet and wood in wet weather. I had anticipated somehow troweling the whole structure smooth, but the finish we ended up with is more like splattered mud. It looks great, but it would be difficult to waterproof. I am also interested in adding insulating straw, plus earthen covering and seeds to grow sod. River Camp doesn't have much soil, mostly river cobbles and gravel, so it will be necessary to import straw and earth if we go that route. I'm in no hurry. We'll figure it out over the next several years, and I'll continue to add to this story. In the meantime, we have a pretty awesome shelter that our students can live in through the coming winter!
Thomas J. Elpel is the author of Living Homes: Stone Masonry, Log, and Strawbale Construction, as well as host of the Slipform Stone Masonry and Build Your Own Masonry Fireplace DVDs. He is the founder and director of Green University®, LLC, "connecting the dots from wilderness survival to sustainable living in the modern world."
See also: Living Homes:
Stone Masonry, Log, and Strawbale Construction.
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